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 $71.62   9.352%   $78.3179   $78.32   $78.30   $78.30  
  Purchase #2 $218.94   10.227%   $241.331   $241.33   $241.35   $241.30  
  Purchase #3 $207.87   10.743%   $230.2015   $230.20   $230.20   $230.20  
  Purchase #4 $53.82   7.837%   $58.0379   $58.04   $58.05   $58.00  
  Purchase #5 $45.27   11.818%   $50.62   $50.62   $50.60   $50.60  
  Purchase #6 $218.62   4.244%   $227.8982   $227.90   $227.90   $227.90  
  Purchase #7 $152.35   5.818%   $161.2137   $161.21   $161.20   $161.20  
  7 purchase totals = $968.49       $1,047.6202   $1,047.62   $1,047.60   $1,047.50