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 $92.25   3.697%   $95.6605   $95.66   $95.65   $95.70  
  Purchase #2 $82.54   8.303%   $89.3933   $89.39   $89.40   $89.40  
  Purchase #3 $111.34   12.310%   $125.046   $125.05   $125.05   $125.00  
  Purchase #4 $84.52   9.743%   $92.7548   $92.75   $92.75   $92.80  
  Purchase #5 $248.78   6.136%   $264.0451   $264.05   $264.05   $264.00  
  Purchase #6 $227.90   3.453%   $235.7694   $235.77   $235.75   $235.80  
  Purchase #7 $179.98   4.208%   $187.5536   $187.55   $187.55   $187.60  
  7 purchase totals = $1,027.31       $1,090.2227   $1,090.22   $1,090.20   $1,090.30