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 $62.93   8.126%   $68.0437   $68.04   $68.05   $68.00  
  Purchase #2 $207.33   6.413%   $220.6261   $220.63   $220.65   $220.60  
  Purchase #3 $52.27   9.413%   $57.1902   $57.19   $57.20   $57.20  
  Purchase #4 $86.48   5.455%   $91.1975   $91.20   $91.20   $91.20  
  Purchase #5 $223.66   12.173%   $250.8861   $250.89   $250.90   $250.90  
  Purchase #6 $83.80   12.661%   $94.4099   $94.41   $94.40   $94.40  
  Purchase #7 $90.41   10.121%   $99.5604   $99.56   $99.55   $99.60  
  7 purchase totals = $806.88       $881.9139   $881.92   $881.95   $881.90