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 $53.78   13.574%   $61.0801   $61.08   $61.10   $61.10  
  Purchase #2 $223.48   7.685%   $240.6544   $240.65   $240.65   $240.70  
  Purchase #3 $96.90   13.532%   $110.0125   $110.01   $110.00   $110.00  
  Purchase #4 $12.29   8.851%   $13.3778   $13.38   $13.40   $13.40  
  Purchase #5 $135.88   5.156%   $142.886   $142.89   $142.90   $142.90  
  Purchase #6 $238.64   10.488%   $263.6686   $263.67   $263.65   $263.70  
  Purchase #7 $209.39   9.115%   $228.4759   $228.48   $228.50   $228.50  
  7 purchase totals = $970.36       $1,060.1553   $1,060.16   $1,060.20   $1,060.30