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 $92.77   12.740%   $104.5889   $104.59   $104.60   $104.60  
  Purchase #2 $144.85   6.328%   $154.0161   $154.02   $154.00   $154.00  
  Purchase #3 $217.78   13.121%   $246.3549   $246.35   $246.35   $246.40  
  Purchase #4 $240.64   9.113%   $262.5695   $262.57   $262.55   $262.60  
  Purchase #5 $10.72   8.569%   $11.6386   $11.64   $11.65   $11.60  
  Purchase #6 $172.50   12.391%   $193.8745   $193.87   $193.85   $193.90  
  Purchase #7 $145.56   13.711%   $165.5177   $165.52   $165.50   $165.50  
  7 purchase totals = $1,024.82       $1,138.5602   $1,138.56   $1,138.50   $1,138.60