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 $184.96   6.709%   $197.369   $197.37   $197.35   $197.40  
  Purchase #2 $12.68   13.483%   $14.3896   $14.39   $14.40   $14.40  
  Purchase #3 $50.67   6.850%   $54.1409   $54.14   $54.15   $54.10  
  Purchase #4 $172.64   6.695%   $184.1982   $184.20   $184.20   $184.20  
  Purchase #5 $212.70   10.595%   $235.2356   $235.24   $235.25   $235.20  
  Purchase #6 $52.64   11.279%   $58.5773   $58.58   $58.60   $58.60  
  Purchase #7 $35.35   11.203%   $39.3103   $39.31   $39.30   $39.30  
  7 purchase totals = $721.64       $783.2209   $783.23   $783.25   $783.20