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 $59.36   13.393%   $67.3101   $67.31   $67.30   $67.30  
  Purchase #2 $137.28   10.530%   $151.7356   $151.74   $151.75   $151.70  
  Purchase #3 $224.53   9.601%   $246.0871   $246.09   $246.10   $246.10  
  Purchase #4 $173.71   11.331%   $193.3931   $193.39   $193.40   $193.40  
  Purchase #5 $50.71   4.669%   $53.0776   $53.08   $53.10   $53.10  
  Purchase #6 $243.52   10.644%   $269.4403   $269.44   $269.45   $269.40  
  Purchase #7 $25.73   12.763%   $29.0139   $29.01   $29.00   $29.00  
  7 purchase totals = $914.84       $1,010.0577   $1,010.06   $1,010.10   $1,010.00