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 $58.68   11.759%   $65.5802   $65.58   $65.60   $65.60  
  Purchase #2 $199.81   5.686%   $211.1712   $211.17   $211.15   $211.20  
  Purchase #3 $209.42   10.740%   $231.9117   $231.91   $231.90   $231.90  
  Purchase #4 $71.29   11.627%   $79.5789   $79.58   $79.60   $79.60  
  Purchase #5 $215.50   12.143%   $241.6682   $241.67   $241.65   $241.70  
  Purchase #6 $6.74   9.360%   $7.3709   $7.37   $7.35   $7.40  
  Purchase #7 $190.67   13.300%   $216.0291   $216.03   $216.05   $216.00  
  7 purchase totals = $952.11       $1,053.3102   $1,053.31   $1,053.30   $1,053.40