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 $83.26   12.782%   $93.9023   $93.90   $93.90   $93.90  
  Purchase #2 $135.64   12.707%   $152.8758   $152.88   $152.90   $152.90  
  Purchase #3 $236.93   3.770%   $245.8623   $245.86   $245.85   $245.90  
  Purchase #4 $56.55   7.133%   $60.5837   $60.58   $60.60   $60.60  
  Purchase #5 $200.31   11.451%   $223.2475   $223.25   $223.25   $223.20  
  Purchase #6 $58.96   5.358%   $62.1191   $62.12   $62.10   $62.10  
  Purchase #7 $168.71   7.139%   $180.7542   $180.75   $180.75   $180.80  
  7 purchase totals = $940.36       $1,019.3449   $1,019.34   $1,019.35   $1,019.40