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 $54.56   13.533%   $61.9436   $61.94   $61.95   $61.90  
  Purchase #2 $165.68   6.152%   $175.8726   $175.87   $175.85   $175.90  
  Purchase #3 $203.51   12.246%   $228.4318   $228.43   $228.45   $228.40  
  Purchase #4 $200.60   9.196%   $219.0472   $219.05   $219.05   $219.00  
  Purchase #5 $118.78   7.192%   $127.3227   $127.32   $127.30   $127.30  
  Purchase #6 $198.49   4.162%   $206.7512   $206.75   $206.75   $206.80  
  Purchase #7 $241.50   5.492%   $254.7632   $254.76   $254.75   $254.80  
  7 purchase totals = $1,183.12       $1,274.1323   $1,274.12   $1,274.10   $1,274.10