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 $216.91   11.413%   $241.6659   $241.67   $241.65   $241.70  
  Purchase #2 $161.52   9.363%   $176.6431   $176.64   $176.65   $176.60  
  Purchase #3 $86.25   8.599%   $93.6666   $93.67   $93.65   $93.70  
  Purchase #4 $205.36   7.804%   $221.3863   $221.39   $221.40   $221.40  
  Purchase #5 $87.36   3.603%   $90.5076   $90.51   $90.50   $90.50  
  Purchase #6 $139.76   5.744%   $147.7878   $147.79   $147.80   $147.80  
  Purchase #7 $203.55   7.735%   $219.2946   $219.29   $219.30   $219.30  
  7 purchase totals = $1,100.71       $1,190.9519   $1,190.96   $1,190.95   $1,191.00