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 $137.78   5.783%   $145.7478   $145.75   $145.75   $145.70  
  Purchase #2 $177.49   11.346%   $197.628   $197.63   $197.65   $197.60  
  Purchase #3 $55.54   11.184%   $61.7516   $61.75   $61.75   $61.80  
  Purchase #4 $69.72   9.445%   $76.3051   $76.31   $76.30   $76.30  
  Purchase #5 $249.52   10.202%   $274.976   $274.98   $275.00   $275.00  
  Purchase #6 $223.89   5.460%   $236.1144   $236.11   $236.10   $236.10  
  Purchase #7 $54.40   9.566%   $59.6039   $59.60   $59.60   $59.60  
  7 purchase totals = $968.34       $1,052.1268   $1,052.13   $1,052.15   $1,052.10