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 $34.66   11.158%   $38.5274   $38.53   $38.55   $38.50  
  Purchase #2 $223.62   11.648%   $249.6673   $249.67   $249.65   $249.70  
  Purchase #3 $225.71   4.539%   $235.955   $235.96   $235.95   $236.00  
  Purchase #4 $46.97   6.717%   $50.125   $50.13   $50.15   $50.10  
  Purchase #5 $70.42   7.646%   $75.8043   $75.80   $75.80   $75.80  
  Purchase #6 $12.95   12.155%   $14.5241   $14.52   $14.50   $14.50  
  Purchase #7 $203.33   10.153%   $223.9741   $223.97   $223.95   $224.00  
  7 purchase totals = $817.66       $888.5772   $888.58   $888.55   $888.60