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 $211.75   4.157%   $220.5524   $220.55   $220.55   $220.60  
  Purchase #2 $205.31   13.741%   $233.5216   $233.52   $233.50   $233.50  
  Purchase #3 $56.77   12.813%   $64.0439   $64.04   $64.05   $64.00  
  Purchase #4 $181.57   4.306%   $189.3884   $189.39   $189.40   $189.40  
  Purchase #5 $185.88   11.131%   $206.5703   $206.57   $206.55   $206.60  
  Purchase #6 $67.73   3.145%   $69.8601   $69.86   $69.85   $69.90  
  Purchase #7 $35.80   10.385%   $39.5178   $39.52   $39.50   $39.50  
  7 purchase totals = $944.81       $1,023.4545   $1,023.45   $1,023.40   $1,023.50