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 $187.43   9.734%   $205.6744   $205.67   $205.65   $205.70  
  Purchase #2 $176.63   6.212%   $187.6023   $187.60   $187.60   $187.60  
  Purchase #3 $67.79   11.358%   $75.4896   $75.49   $75.50   $75.50  
  Purchase #4 $180.85   13.217%   $204.7529   $204.75   $204.75   $204.80  
  Purchase #5 $118.56   11.581%   $132.2904   $132.29   $132.30   $132.30  
  Purchase #6 $230.61   13.862%   $262.5772   $262.58   $262.60   $262.60  
  Purchase #7 $20.86   5.500%   $22.0073   $22.01   $22.00   $22.00  
  7 purchase totals = $982.73       $1,090.3941   $1,090.39   $1,090.40   $1,090.50