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 $97.89   3.801%   $101.6108   $101.61   $101.60   $101.60  
  Purchase #2 $232.68   4.869%   $244.0092   $244.01   $244.00   $244.00  
  Purchase #3 $87.75   10.139%   $96.647   $96.65   $96.65   $96.60  
  Purchase #4 $210.68   13.588%   $239.3072   $239.31   $239.30   $239.30  
  Purchase #5 $225.32   8.109%   $243.5912   $243.59   $243.60   $243.60  
  Purchase #6 $160.73   4.220%   $167.5128   $167.51   $167.50   $167.50  
  Purchase #7 $169.30   12.252%   $190.0426   $190.04   $190.05   $190.00  
  7 purchase totals = $1,184.35       $1,282.7208   $1,282.72   $1,282.70   $1,282.60