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 $85.58   12.690%   $96.4401   $96.44   $96.45   $96.40  
  Purchase #2 $197.46   12.761%   $222.6579   $222.66   $222.65   $222.70  
  Purchase #3 $73.39   3.112%   $75.6739   $75.67   $75.65   $75.70  
  Purchase #4 $170.58   9.868%   $187.4128   $187.41   $187.40   $187.40  
  Purchase #5 $41.52   10.749%   $45.983   $45.98   $46.00   $46.00  
  Purchase #6 $20.74   11.634%   $23.1529   $23.15   $23.15   $23.20  
  Purchase #7 $201.48   5.159%   $211.8744   $211.87   $211.85   $211.90  
  7 purchase totals = $790.75       $863.1950   $863.18   $863.15   $863.30