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 $48.80   8.852%   $53.1198   $53.12   $53.10   $53.10  
  Purchase #2 $202.78   13.591%   $230.3398   $230.34   $230.35   $230.30  
  Purchase #3 $47.57   5.449%   $50.1621   $50.16   $50.15   $50.20  
  Purchase #4 $230.97   7.265%   $247.75   $247.75   $247.75   $247.80  
  Purchase #5 $189.44   10.654%   $209.6229   $209.62   $209.60   $209.60  
  Purchase #6 $156.55   10.177%   $172.4821   $172.48   $172.50   $172.50  
  Purchase #7 $55.42   8.373%   $60.0603   $60.06   $60.05   $60.10  
  7 purchase totals = $931.53       $1,023.5370   $1,023.53   $1,023.50   $1,023.60