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 $54.35   13.241%   $61.5465   $61.55   $61.55   $61.50  
  Purchase #2 $89.63   9.356%   $98.0158   $98.02   $98.00   $98.00  
  Purchase #3 $104.81   5.544%   $110.6207   $110.62   $110.60   $110.60  
  Purchase #4 $65.82   12.337%   $73.9402   $73.94   $73.95   $73.90  
  Purchase #5 $138.68   6.142%   $147.1977   $147.20   $147.20   $147.20  
  Purchase #6 $47.82   7.372%   $51.3453   $51.35   $51.35   $51.30  
  Purchase #7 $41.75   3.779%   $43.3277   $43.33   $43.35   $43.30  
  7 purchase totals = $542.86       $585.9939   $586.01   $586.00   $585.80