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 $41.74   5.133%   $43.8825   $43.88   $43.90   $43.90  
  Purchase #2 $212.63   9.817%   $233.5039   $233.50   $233.50   $233.50  
  Purchase #3 $161.46   12.662%   $181.9041   $181.90   $181.90   $181.90  
  Purchase #4 $43.82   13.139%   $49.5775   $49.58   $49.60   $49.60  
  Purchase #5 $81.79   3.514%   $84.6641   $84.66   $84.65   $84.70  
  Purchase #6 $90.31   5.163%   $94.9727   $94.97   $94.95   $95.00  
  Purchase #7 $146.53   6.185%   $155.5929   $155.59   $155.60   $155.60  
  7 purchase totals = $778.28       $844.0977   $844.08   $844.10   $844.20