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 $59.67   6.656%   $63.6416   $63.64   $63.65   $63.60  
  Purchase #2 $96.28   10.327%   $106.2228   $106.22   $106.20   $106.20  
  Purchase #3 $155.51   3.303%   $160.6465   $160.65   $160.65   $160.60  
  Purchase #4 $219.84   11.284%   $244.6467   $244.65   $244.65   $244.60  
  Purchase #5 $215.71   11.827%   $241.222   $241.22   $241.20   $241.20  
  Purchase #6 $59.36   13.417%   $67.3243   $67.32   $67.30   $67.30  
  Purchase #7 $34.96   13.651%   $39.7324   $39.73   $39.75   $39.70  
  7 purchase totals = $841.33       $923.4363   $923.43   $923.40   $923.20