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 $156.44   10.785%   $173.3121   $173.31   $173.30   $173.30  
  Purchase #2 $67.84   11.144%   $75.4001   $75.40   $75.40   $75.40  
  Purchase #3 $86.27   11.722%   $96.3826   $96.38   $96.40   $96.40  
  Purchase #4 $87.38   12.160%   $98.0054   $98.01   $98.00   $98.00  
  Purchase #5 $210.25   11.809%   $235.0784   $235.08   $235.10   $235.10  
  Purchase #6 $248.43   7.740%   $267.6585   $267.66   $267.65   $267.70  
  Purchase #7 $92.44   11.519%   $103.0882   $103.09   $103.10   $103.10  
  7 purchase totals = $949.05       $1,048.9253   $1,048.93   $1,048.95   $1,049.00