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 $228.98   9.298%   $250.2706   $250.27   $250.25   $250.30  
  Purchase #2 $56.53   6.469%   $60.1869   $60.19   $60.20   $60.20  
  Purchase #3 $140.72   6.678%   $150.1173   $150.12   $150.10   $150.10  
  Purchase #4 $108.79   6.661%   $116.0365   $116.04   $116.05   $116.00  
  Purchase #5 $130.28   3.319%   $134.604   $134.60   $134.60   $134.60  
  Purchase #6 $92.33   11.317%   $102.779   $102.78   $102.80   $102.80  
  Purchase #7 $234.96   6.641%   $250.5637   $250.56   $250.55   $250.60  
  7 purchase totals = $992.59       $1,064.5580   $1,064.56   $1,064.55   $1,064.60