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 $6.26   11.551%   $6.9831   $6.98   $7.00   $7.00  
  Purchase #2 $197.31   3.556%   $204.3263   $204.33   $204.35   $204.30  
  Purchase #3 $67.99   5.736%   $71.8899   $71.89   $71.90   $71.90  
  Purchase #4 $43.45   5.589%   $45.8784   $45.88   $45.90   $45.90  
  Purchase #5 $248.75   11.168%   $276.5304   $276.53   $276.55   $276.50  
  Purchase #6 $195.98   12.173%   $219.8366   $219.84   $219.85   $219.80  
  Purchase #7 $165.98   13.678%   $188.6827   $188.68   $188.70   $188.70  
  7 purchase totals = $925.72       $1,014.1274   $1,014.13   $1,014.25   $1,014.10