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 $205.77   13.117%   $232.7609   $232.76   $232.75   $232.80  
  Purchase #2 $123.56   9.694%   $135.5379   $135.54   $135.55   $135.50  
  Purchase #3 $23.67   12.850%   $26.7116   $26.71   $26.70   $26.70  
  Purchase #4 $180.28   11.467%   $200.9527   $200.95   $200.95   $201.00  
  Purchase #5 $173.96   8.753%   $189.1867   $189.19   $189.20   $189.20  
  Purchase #6 $198.44   13.789%   $225.8029   $225.80   $225.80   $225.80  
  Purchase #7 $88.51   3.810%   $91.8822   $91.88   $91.90   $91.90  
  7 purchase totals = $994.19       $1,102.8349   $1,102.83   $1,102.85   $1,102.90