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 $174.78   12.802%   $197.1553   $197.16   $197.15   $197.20  
  Purchase #2 $76.84   6.720%   $82.0036   $82.00   $82.00   $82.00  
  Purchase #3 $226.79   12.480%   $255.0934   $255.09   $255.10   $255.10  
  Purchase #4 $110.50   5.305%   $116.362   $116.36   $116.35   $116.40  
  Purchase #5 $168.84   5.424%   $177.9979   $178.00   $178.00   $178.00  
  Purchase #6 $129.37   4.119%   $134.6988   $134.70   $134.70   $134.70  
  Purchase #7 $78.74   4.842%   $82.5526   $82.55   $82.55   $82.60  
  7 purchase totals = $965.86       $1,045.8636   $1,045.86   $1,045.85   $1,046.00