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 $78.79   8.530%   $85.5108   $85.51   $85.50   $85.50  
  Purchase #2 $195.83   7.489%   $210.4957   $210.50   $210.50   $210.50  
  Purchase #3 $153.56   11.112%   $170.6236   $170.62   $170.60   $170.60  
  Purchase #4 $207.76   12.130%   $232.9613   $232.96   $232.95   $233.00  
  Purchase #5 $92.37   8.173%   $99.9194   $99.92   $99.90   $99.90  
  Purchase #6 $53.77   4.654%   $56.2725   $56.27   $56.25   $56.30  
  Purchase #7 $161.55   9.616%   $177.0846   $177.08   $177.10   $177.10  
  7 purchase totals = $943.63       $1,032.8679   $1,032.86   $1,032.80   $1,032.90