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 $74.67   10.783%   $82.7217   $82.72   $82.70   $82.70  
  Purchase #2 $232.93   11.854%   $260.5415   $260.54   $260.55   $260.50  
  Purchase #3 $207.98   11.518%   $231.9351   $231.94   $231.95   $231.90  
  Purchase #4 $75.42   11.241%   $83.898   $83.90   $83.90   $83.90  
  Purchase #5 $72.53   9.494%   $79.416   $79.42   $79.40   $79.40  
  Purchase #6 $10.38   7.171%   $11.1243   $11.12   $11.10   $11.10  
  Purchase #7 $56.26   13.753%   $63.9974   $64.00   $64.00   $64.00  
  7 purchase totals = $730.17       $813.6340   $813.64   $813.60   $813.50