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 $197.62   6.148%   $209.7697   $209.77   $209.75   $209.80  
  Purchase #2 $195.80   6.556%   $208.6366   $208.64   $208.65   $208.60  
  Purchase #3 $33.93   12.608%   $38.2079   $38.21   $38.20   $38.20  
  Purchase #4 $169.81   8.363%   $184.0112   $184.01   $184.00   $184.00  
  Purchase #5 $18.33   12.649%   $20.6486   $20.65   $20.65   $20.60  
  Purchase #6 $159.52   11.683%   $178.1567   $178.16   $178.15   $178.20  
  Purchase #7 $151.79   8.844%   $165.2143   $165.21   $165.20   $165.20  
  7 purchase totals = $926.80       $1,004.6450   $1,004.65   $1,004.60   $1,004.60