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 $54.50   12.534%   $61.331   $61.33   $61.35   $61.30  
  Purchase #2 $36.78   13.283%   $41.6655   $41.67   $41.65   $41.70  
  Purchase #3 $177.36   12.673%   $199.8368   $199.84   $199.85   $199.80  
  Purchase #4 $220.43   6.619%   $235.0203   $235.02   $235.00   $235.00  
  Purchase #5 $210.84   5.123%   $221.6413   $221.64   $221.65   $221.60  
  Purchase #6 $149.80   11.611%   $167.1933   $167.19   $167.20   $167.20  
  Purchase #7 $62.78   6.534%   $66.882   $66.88   $66.90   $66.90  
  7 purchase totals = $912.49       $993.5702   $993.57   $993.60   $993.50