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 $54.88   10.278%   $60.5206   $60.52   $60.50   $60.50  
  Purchase #2 $154.34   12.738%   $173.9998   $174.00   $174.00   $174.00  
  Purchase #3 $156.79   3.702%   $162.5944   $162.59   $162.60   $162.60  
  Purchase #4 $232.36   13.407%   $263.5125   $263.51   $263.50   $263.50  
  Purchase #5 $96.35   11.792%   $107.7116   $107.71   $107.70   $107.70  
  Purchase #6 $195.50   5.120%   $205.5096   $205.51   $205.50   $205.50  
  Purchase #7 $120.95   11.480%   $134.8351   $134.84   $134.85   $134.80  
  7 purchase totals = $1,011.17       $1,108.6836   $1,108.68   $1,108.65   $1,108.60