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 $204.87   12.284%   $230.0362   $230.04   $230.05   $230.00  
  Purchase #2 $160.51   13.760%   $182.5962   $182.60   $182.60   $182.60  
  Purchase #3 $127.57   4.199%   $132.9267   $132.93   $132.95   $132.90  
  Purchase #4 $41.41   6.297%   $44.0176   $44.02   $44.00   $44.00  
  Purchase #5 $115.91   9.281%   $126.6676   $126.67   $126.65   $126.70  
  Purchase #6 $216.93   11.372%   $241.5993   $241.60   $241.60   $241.60  
  Purchase #7 $71.89   4.330%   $75.0028   $75.00   $75.00   $75.00  
  7 purchase totals = $939.09       $1,032.8464   $1,032.86   $1,032.85   $1,032.80