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 $105.99   11.535%   $118.2159   $118.22   $118.20   $118.20  
  Purchase #2 $85.30   11.122%   $94.7871   $94.79   $94.80   $94.80  
  Purchase #3 $111.33   8.865%   $121.1994   $121.20   $121.20   $121.20  
  Purchase #4 $75.80   9.600%   $83.0768   $83.08   $83.10   $83.10  
  Purchase #5 $72.33   11.674%   $80.7738   $80.77   $80.75   $80.80  
  Purchase #6 $150.31   3.483%   $155.5453   $155.55   $155.55   $155.50  
  Purchase #7 $150.99   5.676%   $159.5602   $159.56   $159.55   $159.60  
  7 purchase totals = $752.05       $813.1585   $813.17   $813.15   $813.20