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 $95.70   10.333%   $105.5887   $105.59   $105.60   $105.60  
  Purchase #2 $91.37   11.591%   $101.9607   $101.96   $101.95   $102.00  
  Purchase #3 $122.29   3.632%   $126.7316   $126.73   $126.75   $126.70  
  Purchase #4 $221.30   4.836%   $232.0021   $232.00   $232.00   $232.00  
  Purchase #5 $223.99   13.756%   $254.8021   $254.80   $254.80   $254.80  
  Purchase #6 $61.98   4.644%   $64.8584   $64.86   $64.85   $64.90  
  Purchase #7 $203.66   4.177%   $212.1669   $212.17   $212.15   $212.20  
  7 purchase totals = $1,020.29       $1,098.1105   $1,098.11   $1,098.10   $1,098.20