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 $121.41   9.562%   $133.0192   $133.02   $133.00   $133.00  
  Purchase #2 $161.49   12.666%   $181.9443   $181.94   $181.95   $181.90  
  Purchase #3 $14.51   11.673%   $16.2038   $16.20   $16.20   $16.20  
  Purchase #4 $220.42   9.206%   $240.7119   $240.71   $240.70   $240.70  
  Purchase #5 $201.86   12.113%   $226.3113   $226.31   $226.30   $226.30  
  Purchase #6 $153.36   10.284%   $169.1315   $169.13   $169.15   $169.10  
  Purchase #7 $94.48   10.143%   $104.0631   $104.06   $104.05   $104.10  
  7 purchase totals = $967.53       $1,071.3851   $1,071.37   $1,071.35   $1,071.30