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 $184.47   9.822%   $202.5886   $202.59   $202.60   $202.60  
  Purchase #2 $170.43   12.298%   $191.3895   $191.39   $191.40   $191.40  
  Purchase #3 $229.62   12.662%   $258.6945   $258.69   $258.70   $258.70  
  Purchase #4 $61.50   5.736%   $65.0276   $65.03   $65.05   $65.00  
  Purchase #5 $119.79   5.683%   $126.5977   $126.60   $126.60   $126.60  
  Purchase #6 $61.33   4.325%   $63.9825   $63.98   $64.00   $64.00  
  Purchase #7 $129.30   8.519%   $140.3151   $140.32   $140.30   $140.30  
  7 purchase totals = $956.44       $1,048.5955   $1,048.60   $1,048.65   $1,048.60