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 $113.52   13.656%   $129.0223   $129.02   $129.00   $129.00  
  Purchase #2 $116.42   4.777%   $121.9814   $121.98   $122.00   $122.00  
  Purchase #3 $196.66   3.647%   $203.8322   $203.83   $203.85   $203.80  
  Purchase #4 $233.64   11.290%   $260.018   $260.02   $260.00   $260.00  
  Purchase #5 $61.53   9.300%   $67.2523   $67.25   $67.25   $67.30  
  Purchase #6 $107.63   13.655%   $122.3269   $122.33   $122.35   $122.30  
  Purchase #7 $239.74   9.562%   $262.6639   $262.66   $262.65   $262.70  
  7 purchase totals = $1,069.14       $1,167.0970   $1,167.09   $1,167.10   $1,167.10