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 $132.95   9.132%   $145.091   $145.09   $145.10   $145.10  
  Purchase #2 $60.93   3.554%   $63.0955   $63.10   $63.10   $63.10  
  Purchase #3 $125.45   10.160%   $138.1957   $138.20   $138.20   $138.20  
  Purchase #4 $106.92   10.606%   $118.2599   $118.26   $118.25   $118.30  
  Purchase #5 $201.28   5.156%   $211.658   $211.66   $211.65   $211.70  
  Purchase #6 $194.33   11.498%   $216.6741   $216.67   $216.65   $216.70  
  Purchase #7 $75.74   8.294%   $82.0219   $82.02   $82.00   $82.00  
  7 purchase totals = $897.60       $974.9961   $975.00   $974.95   $975.10