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 $61.78   5.441%   $65.1414   $65.14   $65.15   $65.10  
  Purchase #2 $47.66   10.584%   $52.7043   $52.70   $52.70   $52.70  
  Purchase #3 $212.61   4.211%   $221.563   $221.56   $221.55   $221.60  
  Purchase #4 $197.80   11.330%   $220.2107   $220.21   $220.20   $220.20  
  Purchase #5 $209.80   7.198%   $224.9014   $224.90   $224.90   $224.90  
  Purchase #6 $196.98   13.201%   $222.9833   $222.98   $223.00   $223.00  
  Purchase #7 $41.64   6.557%   $44.3703   $44.37   $44.35   $44.40  
  7 purchase totals = $968.27       $1,051.8744   $1,051.86   $1,051.85   $1,051.90