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 $106.39   8.270%   $115.1885   $115.19   $115.20   $115.20  
  Purchase #2 $180.75   5.871%   $191.3618   $191.36   $191.35   $191.40  
  Purchase #3 $75.90   11.596%   $84.7014   $84.70   $84.70   $84.70  
  Purchase #4 $150.79   12.151%   $169.1125   $169.11   $169.10   $169.10  
  Purchase #5 $151.26   5.249%   $159.1996   $159.20   $159.20   $159.20  
  Purchase #6 $212.37   11.136%   $236.0195   $236.02   $236.00   $236.00  
  Purchase #7 $139.86   11.544%   $156.0054   $156.01   $156.00   $156.00  
  7 purchase totals = $1,017.32       $1,111.5887   $1,111.59   $1,111.55   $1,111.60