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 $32.70   13.186%   $37.0118   $37.01   $37.00   $37.00  
  Purchase #2 $195.93   11.727%   $218.9067   $218.91   $218.90   $218.90  
  Purchase #3 $96.93   8.114%   $104.7949   $104.79   $104.80   $104.80  
  Purchase #4 $235.88   11.703%   $263.485   $263.49   $263.50   $263.50  
  Purchase #5 $204.66   11.618%   $228.4374   $228.44   $228.45   $228.40  
  Purchase #6 $133.48   4.624%   $139.6521   $139.65   $139.65   $139.70  
  Purchase #7 $83.52   4.143%   $86.9802   $86.98   $87.00   $87.00  
  7 purchase totals = $983.10       $1,079.2681   $1,079.27   $1,079.30   $1,079.30