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 $166.98   10.229%   $184.0604   $184.06   $184.05   $184.10  
  Purchase #2 $116.48   11.852%   $130.2852   $130.29   $130.30   $130.30  
  Purchase #3 $50.94   9.629%   $55.845   $55.85   $55.85   $55.80  
  Purchase #4 $146.79   3.810%   $152.3827   $152.38   $152.40   $152.40  
  Purchase #5 $33.38   10.415%   $36.8565   $36.86   $36.85   $36.90  
  Purchase #6 $228.94   13.244%   $259.2608   $259.26   $259.25   $259.30  
  Purchase #7 $167.54   8.413%   $181.6351   $181.64   $181.65   $181.60  
  7 purchase totals = $911.05       $1,000.3257   $1,000.34   $1,000.35   $1,000.40