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 $31.31   11.259%   $34.8352   $34.84   $34.85   $34.80  
  Purchase #2 $225.87   10.225%   $248.9652   $248.97   $248.95   $249.00  
  Purchase #3 $248.74   7.727%   $267.9601   $267.96   $267.95   $268.00  
  Purchase #4 $117.26   6.671%   $125.0824   $125.08   $125.10   $125.10  
  Purchase #5 $39.37   13.294%   $44.6038   $44.60   $44.60   $44.60  
  Purchase #6 $209.43   12.554%   $235.7218   $235.72   $235.70   $235.70  
  Purchase #7 $45.48   10.725%   $50.3577   $50.36   $50.35   $50.40  
  7 purchase totals = $917.46       $1,007.5262   $1,007.53   $1,007.50   $1,007.60