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 $178.97   13.240%   $202.6656   $202.67   $202.65   $202.70  
  Purchase #2 $216.88   6.133%   $230.1813   $230.18   $230.20   $230.20  
  Purchase #3 $232.96   7.871%   $251.2963   $251.30   $251.30   $251.30  
  Purchase #4 $165.91   5.873%   $175.6539   $175.65   $175.65   $175.70  
  Purchase #5 $196.57   5.502%   $207.3853   $207.39   $207.40   $207.40  
  Purchase #6 $68.54   9.816%   $75.2679   $75.27   $75.25   $75.30  
  Purchase #7 $57.99   7.262%   $62.2012   $62.20   $62.20   $62.20  
  7 purchase totals = $1,117.82       $1,204.6515   $1,204.66   $1,204.65   $1,204.80