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 $82.67   7.122%   $88.5578   $88.56   $88.55   $88.60  
  Purchase #2 $11.61   5.837%   $12.2877   $12.29   $12.30   $12.30  
  Purchase #3 $201.52   6.193%   $214.0001   $214.00   $214.00   $214.00  
  Purchase #4 $132.38   4.203%   $137.9439   $137.94   $137.95   $137.90  
  Purchase #5 $133.46   7.561%   $143.5509   $143.55   $143.55   $143.60  
  Purchase #6 $226.33   5.344%   $238.4251   $238.43   $238.45   $238.40  
  Purchase #7 $199.51   11.196%   $221.8471   $221.85   $221.85   $221.80  
  7 purchase totals = $987.48       $1,056.6126   $1,056.62   $1,056.65   $1,056.60