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 $221.87   5.771%   $234.6741   $234.67   $234.65   $234.70  
  Purchase #2 $223.45   5.547%   $235.8448   $235.84   $235.85   $235.80  
  Purchase #3 $69.33   6.740%   $74.0028   $74.00   $74.00   $74.00  
  Purchase #4 $80.65   5.558%   $85.1325   $85.13   $85.15   $85.10  
  Purchase #5 $202.53   4.435%   $211.5122   $211.51   $211.50   $211.50  
  Purchase #6 $30.94   11.574%   $34.521   $34.52   $34.50   $34.50  
  Purchase #7 $88.68   8.406%   $96.1344   $96.13   $96.15   $96.10  
  7 purchase totals = $917.45       $971.8218   $971.80   $971.80   $971.70