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 $90.42   3.734%   $93.7963   $93.80   $93.80   $93.80  
  Purchase #2 $154.68   13.743%   $175.9377   $175.94   $175.95   $175.90  
  Purchase #3 $150.84   5.485%   $159.1136   $159.11   $159.10   $159.10  
  Purchase #4 $8.94   8.192%   $9.6724   $9.67   $9.65   $9.70  
  Purchase #5 $228.89   5.822%   $242.216   $242.22   $242.20   $242.20  
  Purchase #6 $181.82   4.726%   $190.4128   $190.41   $190.40   $190.40  
  Purchase #7 $142.39   13.843%   $162.101   $162.10   $162.10   $162.10  
  7 purchase totals = $957.98       $1,033.2498   $1,033.25   $1,033.20   $1,033.20