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 $229.48   5.220%   $241.4589   $241.46   $241.45   $241.50  
  Purchase #2 $218.45   9.272%   $238.7047   $238.70   $238.70   $238.70  
  Purchase #3 $12.55   9.161%   $13.6997   $13.70   $13.70   $13.70  
  Purchase #4 $170.28   5.309%   $179.3202   $179.32   $179.30   $179.30  
  Purchase #5 $141.91   3.137%   $146.3617   $146.36   $146.35   $146.40  
  Purchase #6 $33.72   8.307%   $36.5211   $36.52   $36.50   $36.50  
  Purchase #7 $161.64   3.487%   $167.2764   $167.28   $167.30   $167.30  
  7 purchase totals = $968.03       $1,023.3427   $1,023.34   $1,023.30   $1,023.40