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 $93.88   8.523%   $101.8814   $101.88   $101.90   $101.90  
  Purchase #2 $16.30   12.663%   $18.3641   $18.36   $18.35   $18.40  
  Purchase #3 $148.84   6.676%   $158.7766   $158.78   $158.80   $158.80  
  Purchase #4 $226.61   13.618%   $257.4697   $257.47   $257.45   $257.50  
  Purchase #5 $50.91   6.385%   $54.1606   $54.16   $54.15   $54.20  
  Purchase #6 $195.97   3.637%   $203.0974   $203.10   $203.10   $203.10  
  Purchase #7 $228.58   5.476%   $241.097   $241.10   $241.10   $241.10  
  7 purchase totals = $961.09       $1,034.8468   $1,034.85   $1,034.85   $1,035.00