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 $58.65   12.444%   $65.9484   $65.95   $65.95   $65.90  
  Purchase #2 $83.50   4.745%   $87.4621   $87.46   $87.45   $87.50  
  Purchase #3 $102.44   4.531%   $107.0816   $107.08   $107.10   $107.10  
  Purchase #4 $109.61   3.727%   $113.6952   $113.70   $113.70   $113.70  
  Purchase #5 $76.43   5.644%   $80.7437   $80.74   $80.75   $80.70  
  Purchase #6 $131.86   13.332%   $149.4396   $149.44   $149.45   $149.40  
  Purchase #7 $209.95   13.347%   $237.972   $237.97   $237.95   $238.00  
  7 purchase totals = $772.44       $842.3426   $842.34   $842.35   $842.30