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 $53.50   13.551%   $60.7498   $60.75   $60.75   $60.70  
  Purchase #2 $163.64   4.630%   $171.2165   $171.22   $171.20   $171.20  
  Purchase #3 $24.51   6.504%   $26.1041   $26.10   $26.10   $26.10  
  Purchase #4 $135.91   5.276%   $143.0806   $143.08   $143.10   $143.10  
  Purchase #5 $151.92   5.619%   $160.4564   $160.46   $160.45   $160.50  
  Purchase #6 $99.92   11.658%   $111.5687   $111.57   $111.55   $111.60  
  Purchase #7 $69.65   8.536%   $75.5953   $75.60   $75.60   $75.60  
  7 purchase totals = $699.05       $748.7714   $748.78   $748.75   $748.80