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 $54.66   7.399%   $58.7043   $58.70   $58.70   $58.70  
  Purchase #2 $216.49   12.484%   $243.5166   $243.52   $243.50   $243.50  
  Purchase #3 $44.69   9.688%   $49.0196   $49.02   $49.00   $49.00  
  Purchase #4 $22.74   11.260%   $25.3005   $25.30   $25.30   $25.30  
  Purchase #5 $166.41   5.668%   $175.8421   $175.84   $175.85   $175.80  
  Purchase #6 $111.71   10.801%   $123.7758   $123.78   $123.80   $123.80  
  Purchase #7 $126.67   3.852%   $131.5493   $131.55   $131.55   $131.50  
  7 purchase totals = $743.37       $807.7082   $807.71   $807.70   $807.60