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 $93.86   12.522%   $105.6131   $105.61   $105.60   $105.60  
  Purchase #2 $60.61   6.842%   $64.7569   $64.76   $64.75   $64.80  
  Purchase #3 $122.79   13.166%   $138.9565   $138.96   $138.95   $139.00  
  Purchase #4 $212.95   10.600%   $235.5227   $235.52   $235.50   $235.50  
  Purchase #5 $52.45   3.108%   $54.0801   $54.08   $54.10   $54.10  
  Purchase #6 $237.28   12.692%   $267.3956   $267.40   $267.40   $267.40  
  Purchase #7 $238.92   6.314%   $254.0054   $254.01   $254.00   $254.00  
  7 purchase totals = $1,018.86       $1,120.3303   $1,120.34   $1,120.30   $1,120.40