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 $191.95   12.592%   $216.1203   $216.12   $216.10   $216.10  
  Purchase #2 $134.79   12.373%   $151.4676   $151.47   $151.45   $151.50  
  Purchase #3 $235.28   10.224%   $259.335   $259.34   $259.35   $259.30  
  Purchase #4 $199.46   9.558%   $218.5244   $218.52   $218.50   $218.50  
  Purchase #5 $33.96   4.818%   $35.5962   $35.60   $35.60   $35.60  
  Purchase #6 $204.76   9.832%   $224.892   $224.89   $224.90   $224.90  
  Purchase #7 $79.54   9.429%   $87.0398   $87.04   $87.05   $87.00  
  7 purchase totals = $1,079.74       $1,192.9753   $1,192.98   $1,192.95   $1,192.90