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 $238.34   13.487%   $270.4849   $270.48   $270.50   $270.50  
  Purchase #2 $22.98   12.751%   $25.9102   $25.91   $25.90   $25.90  
  Purchase #3 $99.53   3.123%   $102.6383   $102.64   $102.65   $102.60  
  Purchase #4 $163.26   12.282%   $183.3116   $183.31   $183.30   $183.30  
  Purchase #5 $167.62   9.788%   $184.0266   $184.03   $184.05   $184.00  
  Purchase #6 $245.57   7.483%   $263.946   $263.95   $263.95   $263.90  
  Purchase #7 $165.71   5.218%   $174.3567   $174.36   $174.35   $174.40  
  7 purchase totals = $1,103.01       $1,204.6743   $1,204.68   $1,204.70   $1,204.60