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 $177.69   11.291%   $197.753   $197.75   $197.75   $197.80  
  Purchase #2 $6.46   8.570%   $7.0136   $7.01   $7.00   $7.00  
  Purchase #3 $173.25   6.263%   $184.1006   $184.10   $184.10   $184.10  
  Purchase #4 $29.98   9.424%   $32.8053   $32.81   $32.80   $32.80  
  Purchase #5 $179.53   8.731%   $195.2048   $195.20   $195.20   $195.20  
  Purchase #6 $221.38   9.627%   $242.6923   $242.69   $242.70   $242.70  
  Purchase #7 $110.47   8.732%   $120.1162   $120.12   $120.10   $120.10  
  7 purchase totals = $898.76       $979.6858   $979.68   $979.65   $979.70