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 $124.98   7.805%   $134.7347   $134.73   $134.75   $134.70  
  Purchase #2 $51.39   4.354%   $53.6275   $53.63   $53.65   $53.60  
  Purchase #3 $240.67   4.615%   $251.7769   $251.78   $251.80   $251.80  
  Purchase #4 $165.31   6.398%   $175.8865   $175.89   $175.90   $175.90  
  Purchase #5 $229.47   6.336%   $244.0092   $244.01   $244.00   $244.00  
  Purchase #6 $143.79   12.299%   $161.4747   $161.47   $161.45   $161.50  
  Purchase #7 $9.84   9.487%   $10.7735   $10.77   $10.75   $10.80  
  7 purchase totals = $965.45       $1,032.2830   $1,032.28   $1,032.30   $1,032.30