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 $236.49   5.398%   $249.2557   $249.26   $249.25   $249.30  
  Purchase #2 $145.82   9.603%   $159.8231   $159.82   $159.80   $159.80  
  Purchase #3 $44.32   3.735%   $45.9754   $45.98   $46.00   $46.00  
  Purchase #4 $120.53   11.590%   $134.4994   $134.50   $134.50   $134.50  
  Purchase #5 $193.58   4.159%   $201.631   $201.63   $201.65   $201.60  
  Purchase #6 $204.65   3.279%   $211.3605   $211.36   $211.35   $211.40  
  Purchase #7 $48.52   3.414%   $50.1765   $50.18   $50.20   $50.20  
  7 purchase totals = $993.91       $1,052.7216   $1,052.73   $1,052.75   $1,052.80