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 $60.52   13.751%   $68.8421   $68.84   $68.85   $68.80  
  Purchase #2 $69.29   9.322%   $75.7492   $75.75   $75.75   $75.70  
  Purchase #3 $234.31   6.595%   $249.7627   $249.76   $249.75   $249.80  
  Purchase #4 $207.50   5.711%   $219.3503   $219.35   $219.35   $219.40  
  Purchase #5 $106.96   13.819%   $121.7408   $121.74   $121.75   $121.70  
  Purchase #6 $189.50   4.284%   $197.6182   $197.62   $197.60   $197.60  
  Purchase #7 $185.50   9.274%   $202.7033   $202.70   $202.70   $202.70  
  7 purchase totals = $1,053.58       $1,135.7666   $1,135.76   $1,135.75   $1,135.70