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 $195.53   5.454%   $206.1942   $206.19   $206.20   $206.20  
  Purchase #2 $174.82   12.704%   $197.0291   $197.03   $197.05   $197.00  
  Purchase #3 $155.30   9.251%   $169.6668   $169.67   $169.65   $169.70  
  Purchase #4 $121.86   11.385%   $135.7338   $135.73   $135.75   $135.70  
  Purchase #5 $33.57   11.505%   $37.4322   $37.43   $37.45   $37.40  
  Purchase #6 $201.27   13.484%   $228.4092   $228.41   $228.40   $228.40  
  Purchase #7 $16.84   7.281%   $18.0661   $18.07   $18.05   $18.10  
  7 purchase totals = $899.19       $992.5314   $992.53   $992.55   $992.50