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 $176.60   12.273%   $198.2741   $198.27   $198.25   $198.30  
  Purchase #2 $56.74   12.349%   $63.7468   $63.75   $63.75   $63.70  
  Purchase #3 $83.79   13.630%   $95.2106   $95.21   $95.20   $95.20  
  Purchase #4 $90.51   12.662%   $101.9704   $101.97   $101.95   $102.00  
  Purchase #5 $181.38   10.688%   $200.7659   $200.77   $200.75   $200.80  
  Purchase #6 $66.85   12.281%   $75.0598   $75.06   $75.05   $75.10  
  Purchase #7 $242.41   10.420%   $267.6691   $267.67   $267.65   $267.70  
  7 purchase totals = $898.28       $1,002.6967   $1,002.70   $1,002.60   $1,002.80