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 $92.39   11.444%   $102.9631   $102.96   $102.95   $103.00  
  Purchase #2 $70.73   4.622%   $73.9991   $74.00   $74.00   $74.00  
  Purchase #3 $25.35   5.174%   $26.6616   $26.66   $26.65   $26.70  
  Purchase #4 $96.40   7.492%   $103.6223   $103.62   $103.60   $103.60  
  Purchase #5 $116.55   11.804%   $130.3076   $130.31   $130.30   $130.30  
  Purchase #6 $228.66   7.746%   $246.372   $246.37   $246.35   $246.40  
  Purchase #7 $228.52   12.683%   $257.5032   $257.50   $257.50   $257.50  
  7 purchase totals = $858.60       $941.4289   $941.42   $941.35   $941.50