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 $116.35   3.794%   $120.7643   $120.76   $120.75   $120.80  
  Purchase #2 $12.65   8.328%   $13.7035   $13.70   $13.70   $13.70  
  Purchase #3 $242.39   11.325%   $269.8407   $269.84   $269.85   $269.80  
  Purchase #4 $177.68   13.377%   $201.4483   $201.45   $201.45   $201.40  
  Purchase #5 $214.43   9.793%   $235.4291   $235.43   $235.45   $235.40  
  Purchase #6 $54.80   8.479%   $59.4465   $59.45   $59.45   $59.40  
  Purchase #7 $57.41   13.696%   $65.2729   $65.27   $65.25   $65.30  
  7 purchase totals = $875.71       $965.9053   $965.90   $965.90   $965.80