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 $57.97   10.733%   $64.1919   $64.19   $64.20   $64.20  
  Purchase #2 $46.39   9.589%   $50.8383   $50.84   $50.85   $50.80  
  Purchase #3 $210.31   9.567%   $230.4304   $230.43   $230.45   $230.40  
  Purchase #4 $56.77   3.129%   $58.5463   $58.55   $58.55   $58.50  
  Purchase #5 $163.61   6.268%   $173.8651   $173.87   $173.85   $173.90  
  Purchase #6 $183.99   10.172%   $202.7055   $202.71   $202.70   $202.70  
  Purchase #7 $219.52   9.799%   $241.0308   $241.03   $241.05   $241.00  
  7 purchase totals = $938.56       $1,021.6083   $1,021.62   $1,021.65   $1,021.50