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 $82.97   11.279%   $92.3282   $92.33   $92.35   $92.30  
  Purchase #2 $114.62   10.510%   $126.6666   $126.67   $126.65   $126.70  
  Purchase #3 $138.80   4.769%   $145.4194   $145.42   $145.40   $145.40  
  Purchase #4 $108.60   12.612%   $122.2966   $122.30   $122.30   $122.30  
  Purchase #5 $210.61   12.141%   $236.1802   $236.18   $236.20   $236.20  
  Purchase #6 $8.87   9.323%   $9.697   $9.70   $9.70   $9.70  
  Purchase #7 $183.52   9.146%   $200.3047   $200.30   $200.30   $200.30  
  7 purchase totals = $847.99       $932.8927   $932.90   $932.90   $932.90