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 $228.67   5.522%   $241.2972   $241.30   $241.30   $241.30  
  Purchase #2 $25.76   5.829%   $27.2616   $27.26   $27.25   $27.30  
  Purchase #3 $81.89   6.614%   $87.3062   $87.31   $87.30   $87.30  
  Purchase #4 $98.39   6.843%   $105.1228   $105.12   $105.10   $105.10  
  Purchase #5 $217.72   5.665%   $230.0538   $230.05   $230.05   $230.10  
  Purchase #6 $242.71   7.229%   $260.2555   $260.26   $260.25   $260.30  
  Purchase #7 $189.57   9.617%   $207.8009   $207.80   $207.80   $207.80  
  7 purchase totals = $1,084.71       $1,159.0980   $1,159.10   $1,159.05   $1,159.20