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 $232.35   7.713%   $250.2712   $250.27   $250.25   $250.30  
  Purchase #2 $114.79   3.392%   $118.6837   $118.68   $118.70   $118.70  
  Purchase #3 $216.44   3.396%   $223.7903   $223.79   $223.80   $223.80  
  Purchase #4 $243.72   12.738%   $274.7651   $274.77   $274.75   $274.80  
  Purchase #5 $136.59   9.325%   $149.327   $149.33   $149.35   $149.30  
  Purchase #6 $250.83   9.614%   $274.9448   $274.94   $274.95   $274.90  
  Purchase #7 $54.30   8.628%   $58.985   $58.99   $59.00   $59.00  
  7 purchase totals = $1,249.02       $1,350.7671   $1,350.77   $1,350.80   $1,350.80