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 $118.98   12.780%   $134.1856   $134.19   $134.20   $134.20  
  Purchase #2 $88.97   13.693%   $101.1527   $101.15   $101.15   $101.20  
  Purchase #3 $204.74   12.594%   $230.525   $230.53   $230.55   $230.50  
  Purchase #4 $34.76   13.633%   $39.4988   $39.50   $39.50   $39.50  
  Purchase #5 $113.39   7.265%   $121.6278   $121.63   $121.65   $121.60  
  Purchase #6 $171.96   12.634%   $193.6854   $193.69   $193.70   $193.70  
  Purchase #7 $201.48   5.266%   $212.0899   $212.09   $212.10   $212.10  
  7 purchase totals = $934.28       $1,032.7652   $1,032.78   $1,032.85   $1,032.80