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 $116.60   11.761%   $130.3133   $130.31   $130.30   $130.30  
  Purchase #2 $190.93   6.227%   $202.8192   $202.82   $202.80   $202.80  
  Purchase #3 $235.61   11.685%   $263.141   $263.14   $263.15   $263.10  
  Purchase #4 $34.35   6.736%   $36.6638   $36.66   $36.65   $36.70  
  Purchase #5 $7.85   11.819%   $8.7778   $8.78   $8.80   $8.80  
  Purchase #6 $34.44   8.288%   $37.2944   $37.29   $37.30   $37.30  
  Purchase #7 $238.34   13.710%   $271.0164   $271.02   $271.00   $271.00  
  7 purchase totals = $858.12       $950.0259   $950.02   $950.00   $950.00