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 $143.65   13.679%   $163.2999   $163.30   $163.30   $163.30  
  Purchase #2 $190.95   6.187%   $202.7641   $202.76   $202.75   $202.80  
  Purchase #3 $102.67   13.625%   $116.6588   $116.66   $116.65   $116.70  
  Purchase #4 $52.45   10.725%   $58.0753   $58.08   $58.10   $58.10  
  Purchase #5 $144.34   3.228%   $148.9993   $149.00   $149.00   $149.00  
  Purchase #6 $234.39   12.132%   $262.8262   $262.83   $262.85   $262.80  
  Purchase #7 $74.48   8.189%   $80.5792   $80.58   $80.60   $80.60  
  7 purchase totals = $942.93       $1,033.2028   $1,033.21   $1,033.25   $1,033.30