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 $111.96   12.334%   $125.7691   $125.77   $125.75   $125.80  
  Purchase #2 $107.80   13.865%   $122.7465   $122.75   $122.75   $122.70  
  Purchase #3 $160.36   6.360%   $170.5589   $170.56   $170.55   $170.60  
  Purchase #4 $29.52   11.294%   $32.854   $32.85   $32.85   $32.90  
  Purchase #5 $141.25   4.694%   $147.8803   $147.88   $147.90   $147.90  
  Purchase #6 $21.65   12.695%   $24.3985   $24.40   $24.40   $24.40  
  Purchase #7 $63.31   9.603%   $69.3897   $69.39   $69.40   $69.40  
  7 purchase totals = $635.85       $693.5970   $693.60   $693.60   $693.70