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 $209.84   5.844%   $222.103   $222.10   $222.10   $222.10  
  Purchase #2 $201.79   11.619%   $225.236   $225.24   $225.25   $225.20  
  Purchase #3 $120.82   7.354%   $129.7051   $129.71   $129.70   $129.70  
  Purchase #4 $90.93   5.582%   $96.0057   $96.01   $96.00   $96.00  
  Purchase #5 $160.61   4.135%   $167.2512   $167.25   $167.25   $167.30  
  Purchase #6 $37.96   6.395%   $40.3875   $40.39   $40.40   $40.40  
  Purchase #7 $209.31   12.377%   $235.2163   $235.22   $235.20   $235.20  
  7 purchase totals = $1,031.26       $1,115.9048   $1,115.92   $1,115.90   $1,115.90