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 $83.40   12.870%   $94.1336   $94.13   $94.15   $94.10  
  Purchase #2 $92.31   4.123%   $96.1159   $96.12   $96.10   $96.10  
  Purchase #3 $152.93   13.348%   $173.3431   $173.34   $173.35   $173.30  
  Purchase #4 $197.32   9.738%   $216.535   $216.54   $216.55   $216.50  
  Purchase #5 $235.75   8.109%   $254.867   $254.87   $254.85   $254.90  
  Purchase #6 $105.59   7.314%   $113.3129   $113.31   $113.30   $113.30  
  Purchase #7 $62.47   6.432%   $66.4881   $66.49   $66.50   $66.50  
  7 purchase totals = $929.77       $1,014.7956   $1,014.80   $1,014.80   $1,014.70