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 $50.33   4.513%   $52.6014   $52.60   $52.60   $52.60  
  Purchase #2 $165.41   11.569%   $184.5463   $184.55   $184.55   $184.50  
  Purchase #3 $167.59   10.401%   $185.021   $185.02   $185.00   $185.00  
  Purchase #4 $201.31   11.874%   $225.2135   $225.21   $225.20   $225.20  
  Purchase #5 $77.43   9.776%   $84.9996   $85.00   $85.00   $85.00  
  Purchase #6 $207.61   8.217%   $224.6693   $224.67   $224.65   $224.70  
  Purchase #7 $83.90   11.362%   $93.4327   $93.43   $93.45   $93.40  
  7 purchase totals = $953.58       $1,050.4838   $1,050.48   $1,050.45   $1,050.40