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 $58.46   5.753%   $61.8232   $61.82   $61.80   $61.80  
  Purchase #2 $185.92   13.795%   $211.5677   $211.57   $211.55   $211.60  
  Purchase #3 $224.72   3.723%   $233.0863   $233.09   $233.10   $233.10  
  Purchase #4 $53.45   12.297%   $60.0227   $60.02   $60.00   $60.00  
  Purchase #5 $144.45   6.422%   $153.7266   $153.73   $153.75   $153.70  
  Purchase #6 $81.68   6.460%   $86.9565   $86.96   $86.95   $87.00  
  Purchase #7 $223.47   8.804%   $243.1443   $243.14   $243.15   $243.10  
  7 purchase totals = $972.15       $1,050.3273   $1,050.33   $1,050.30   $1,050.30