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 $101.28   8.457%   $109.8452   $109.85   $109.85   $109.80  
  Purchase #2 $185.30   13.747%   $210.7732   $210.77   $210.75   $210.80  
  Purchase #3 $124.70   12.707%   $140.5456   $140.55   $140.55   $140.50  
  Purchase #4 $43.33   5.579%   $45.7474   $45.75   $45.75   $45.70  
  Purchase #5 $139.57   11.532%   $155.6652   $155.67   $155.65   $155.70  
  Purchase #6 $203.67   7.518%   $218.9819   $218.98   $219.00   $219.00  
  Purchase #7 $50.65   13.336%   $57.4047   $57.40   $57.40   $57.40  
  7 purchase totals = $848.50       $938.9632   $938.97   $938.95   $938.90