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 $104.98   8.227%   $113.6167   $113.62   $113.60   $113.60  
  Purchase #2 $111.74   5.839%   $118.2645   $118.26   $118.25   $118.30  
  Purchase #3 $160.33   13.330%   $181.702   $181.70   $181.70   $181.70  
  Purchase #4 $81.28   9.240%   $88.7903   $88.79   $88.80   $88.80  
  Purchase #5 $199.62   9.779%   $219.1408   $219.14   $219.15   $219.10  
  Purchase #6 $185.58   9.188%   $202.6311   $202.63   $202.65   $202.60  
  Purchase #7 $151.47   12.257%   $170.0357   $170.04   $170.05   $170.00  
  7 purchase totals = $995.00       $1,094.1811   $1,094.18   $1,094.20   $1,094.10