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 $71.61   5.684%   $75.6803   $75.68   $75.70   $75.70  
  Purchase #2 $209.40   8.739%   $227.6995   $227.70   $227.70   $227.70  
  Purchase #3 $132.96   11.243%   $147.9087   $147.91   $147.90   $147.90  
  Purchase #4 $70.82   11.689%   $79.0981   $79.10   $79.10   $79.10  
  Purchase #5 $216.65   13.526%   $245.9541   $245.95   $245.95   $246.00  
  Purchase #6 $169.92   5.559%   $179.3659   $179.37   $179.35   $179.40  
  Purchase #7 $102.92   8.412%   $111.5776   $111.58   $111.60   $111.60  
  7 purchase totals = $974.28       $1,067.2842   $1,067.29   $1,067.30   $1,067.40