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 $49.92   3.349%   $51.5918   $51.59   $51.60   $51.60  
  Purchase #2 $121.41   3.495%   $125.6533   $125.65   $125.65   $125.70  
  Purchase #3 $145.69   13.809%   $165.8083   $165.81   $165.80   $165.80  
  Purchase #4 $55.82   7.282%   $59.8848   $59.88   $59.90   $59.90  
  Purchase #5 $73.41   5.562%   $77.4931   $77.49   $77.50   $77.50  
  Purchase #6 $121.93   11.407%   $135.8386   $135.84   $135.85   $135.80  
  Purchase #7 $155.41   7.593%   $167.2103   $167.21   $167.20   $167.20  
  7 purchase totals = $723.59       $783.4802   $783.47   $783.50   $783.50