Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $151.89   13.731%   $172.746   $172.75   $172.75   $172.70  
  Purchase #2 $226.43   10.410%   $250.0014   $250.00   $250.00   $250.00  
  Purchase #3 $204.80   13.508%   $232.4644   $232.46   $232.45   $232.50  
  Purchase #4 $246.33   7.563%   $264.9599   $264.96   $264.95   $265.00  
  Purchase #5 $176.68   9.714%   $193.8427   $193.84   $193.85   $193.80  
  Purchase #6 $211.51   11.573%   $235.9881   $235.99   $236.00   $236.00  
  Purchase #7 $102.58   9.783%   $112.6154   $112.62   $112.60   $112.60  
  7 purchase totals = $1,320.22       $1,462.6179   $1,462.62   $1,462.60   $1,462.60