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 $120.69   11.864%   $135.0087   $135.01   $135.00   $135.00  
  Purchase #2 $98.63   4.345%   $102.9155   $102.92   $102.90   $102.90  
  Purchase #3 $25.70   12.379%   $28.8814   $28.88   $28.90   $28.90  
  Purchase #4 $190.45   13.513%   $216.1855   $216.19   $216.20   $216.20  
  Purchase #5 $230.32   5.825%   $243.7361   $243.74   $243.75   $243.70  
  Purchase #6 $107.52   11.135%   $119.4924   $119.49   $119.50   $119.50  
  Purchase #7 $174.96   6.641%   $186.5791   $186.58   $186.60   $186.60  
  7 purchase totals = $948.27       $1,032.7987   $1,032.81   $1,032.85   $1,032.80